Cytotoxic T cells (CTLs) include those capable of recognizing a complex by a specific T cell receptor (hereinafter simply referred to as “TCR”), the complex that is a conjugate of a major histocompatibility gene complex (hereinafter simply referred to as “MHC”)-encoding major histocompatibility antigen molecule (MEC molecule; in a case of human, it is called “human leukocyte antigen,” hereinafter simply referred to as “HLA”) and an antigen peptide, and killing a cell in which the complex is presented on a cell surface. Therefore, in order to establish the cytotoxic reaction, it is necessary that 1) a CTL having a TCR specific to HLA Class I type of a target cell exists, and 2) an antigen peptide so that a complex formed by binding to the HLA molecule is capable of being recognized by the TCR exists.
The antigen peptide as described above is generated by, for example, processing an antigen or the like synthesized in a cell of a mammalian cell in a cytoplasm, thereby degrading into small peptides. The small peptides are further associated with an HLA molecule to be presented on the cell surface. In other words, in the proteasome complex consisting of numerous subunits, a protein is degraded into peptides consisting of 8 to 15 amino acids, some of which are transported from the cytoplasm to the endoplasmic reticulum by a TAP transporter. Once these peptides can be bound to a heterodimer of Class I/β2 microglobulin, they are stabilized in the form of a trimolecular complex, and transported to the cell surface through the Golgi apparatus. A tumor cell expressing a tumor-associated antigen or tumor-specific antigenic protein is supposedly capable of presenting an HLA-restricted antigenic peptide recognized by a T cell.
It has been known that the HLA Class I molecules are mainly HLA-A, -B, and -C, that the antigen peptides which are presented by binding to these molecules consist of 8 to 10 amino acids, and further that there are given different structural features for each of the HLA molecules. For example, as a peptide binding to an HLA-A2.1 molecule which is most frequently found worldwide, a peptide consisting of 9 to 10 amino acids, the peptide having Leu at a second position from an N-terminal, and Leu or Val at a C terminal has been most well known. In addition, as a peptide binding to an HLA-A24 molecule which is found more richly in the Asians such as the Japanese, a peptide consisting of 9 to 10 amino acids, the peptide having any one of Tyr, Phe, Met, and Trp at a second position from an N-terminal, and any one of Leu, Ile, Trp, and Phe at a C-terminal has been most well known.
Tumor antigens for which antigen peptides have so far been identified are MAGE-A 1, MAGE-A3, and MAGE-A4 against HLA-A 1; MAGE-A3, MART1, tyrosinase, gp100, HER2/neu, CEA and the like against HLA-A2.1; MAGE-A3 against HLA-Cwl; MAGE-A3 against HLA-B44; MAGE-A4 against HLA-B37; and MAGE-A1, MAGE-A2, MAGE-A3, MAGE-A4, NY-ESO-1, CEA, HER2/neu, tyrosinase, β-catenin, and the like against HLA-A24. In many of these tumor antigens, first, a cell line is established for a Class I-restricted CTL recognizing a tumor cell, a tumor antigen recognized by the CTL is identified, a minimum unit in tumor antigen proteins is subsequently found by a genetic engineering method, and peptides in the minimum unit are further found on the basis of the information regarding the binding motif to the HLA Class I molecules. In addition, first, peptides binding to the HLA Class I molecules are found in the tumor antigen proteins on the basis of the motif structure commonly shared between the above-mentioned peptides binding to the HLA Class I molecules, those peptides from which CTLs are inducible are subsequently selected utilizing an antigen presenting cell, and finally antigen peptides are then determined depending upon whether or not a CTL having toxicity against a tumor cell can be induced.
On the other hand, the HLA Class I molecules are classified into some subtypes, and the kinds of owned subtypes greatly differ among races. Worldwide, HLA-A2 is most often found, and 45% of the Caucasians are HLA-A2-positive. Moreover, the identification of this HLA-A2-restricted antigen peptide is most advanced. In the Japanese, HLA-A2-positive is found in 40%, and when their subtypes are studied, HLA-A*0201-positive, which is the same as the Caucasians, is 20%, and much of the remaining are A*0206-positive. The binding peptides to these subtypes are different, so that HLA-A2 that is mainly studied is HLA-A*0201. On the other hand, in the Japanese, HLA-A24-positive is found in 60% or more, and an HLA-A24-positive percentage is higher in the Asians than other races. Therefore, the finding of an HLA-A24-restricted antigen peptide plays an important role in providing a CTL that is useful in the treatment of tumor by inducing a CTL acting specifically to a tumor cell in the Asians, especially the Japanese.
Since antigen peptides differ on the basis of the difference in the HLA even with the same antigen, the induction of a CTL utilizing antigen peptides is complicated. Although various contrivances have been made in order to solve this disadvantage, a satisfactory fruit has not yet been obtained. One contrivance is a method including the steps of transducing an antigenic gene into an antigen presenting cell derived from a patient him/herself (self), and inducing a T cell utilizing the transformed gene. As the antigen presenting cell, B cell, macrophage, and dendritic cell have been studied, and a clinical test has been carried out using as an adjuvant or the like for a vaccine centering about dendritic cell which is known as a professional antigen presenting cell. However, there is a disadvantage that much labor is required in furnishing these antigen presenting cells in an amount necessary for immune induction. B cell can be mass-produced by immortalization by EB virus; however, there is a disadvantage in safety from the viewpoint of use of a virus.
As tumor antigen-specific TCR genes, for example, genes such as HLA-A2-restricted, MART1-specific TCR [Non-Patent Publication 1], MAGE-A3-specific TCR [Non-Patent Publication 2], CAMEL (CTL-recognized antigen on melanoma)-specific TCR [Non-Patent Publication 3], gp100-specific TCR [Non-Patent Publication 4], NY-ESO-1-specific TCR [Non-Patent Publication 5], HLA-24-restricted WT1 (Wilms tumor 1)-specific TCR [Non-Patent Publication 6], HLA-Cw16-restricted MAGE-A1-specific TCR [Non-Patent Publication 7] have been cloned.
It can be expected to give a specific cytotoxic activity to an intended antigen by transducing TCR gene into a given CTL. Based on the above, gene therapies with TCR gene targeted to MART1 [Non-Patent Publication 8], gp100 [Non-Patent Publication 4] and mHAG HA-2 antigen [Non-Patent Publication 9] have been tried.
MAGE-A4 is an antigen belonging to a MAGE subfamily of a cancer-testis antigen family, which is expressed in various cancers and has a high antigenicity (positive in 60% of esophageal cancer, 50% of head and neck cancers, 24% of non-small cell pulmonary cancer, 33% of stomach cancer, and 21% of Hodgkin disease), so that the antigen is expected to serve as a target antigen in cancer vaccine therapy. An HLA-A24-restricted MAGE-A4143-151 peptide-specific CTL clone has been obtained [Non-Patent Publication 10].    Non-Patent Publication 1: Cancer Res., 54, 5265-5268 (1994)    Non-Patent Publication 2: Anticancer Res., 20, 1793-1799 (2000)    Non-Patent Publication 3: Int. J. Cancer, 99, 7-13 (2002)    Non-Patent Publication 4: J. Immunol. 170, 2186-2194 (2003)    Non-Patent Publication 5: J. Immunol., 174, 4415-4423 (2005)    Non-Patent Publication 6: Blood, 106, 470-476 (2005)    Non-Patent Publication 7: Int. Immunol., 8, 1463-1466 (1996)    Non-Patent Publication 8: J. Immunol., 163, 507-513 (1999)    Non-Patent Publication 9: Blood, 103, 3530-3540 (2003)    Non-Patent Publication 10: Clin. Cancer Res., 11, 5581-5589 (2005)